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I Forge Iron

How small can a n/a burner be?


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I have seen mention of smaller-than-3/4" burners a few times now and when I have some spare time, want to bench race a couple ideas. The question I have, however is just how small can you go and actually have a workable flame i.e. how small can you go with the naturally aspirated theory before the tube size to molecule size begins to break down. I see it a lot on miniature water scenes especially in old movies b4 cgi came along. A miniature battle ship just doesn't float the same way a full sized one does due to the size of the model to the size of water molecules. I guess the best term would be viscosity(?)
How viscous can the air fuel mix; how close can those molecules be jammed together in a tube? Anybody build a 3/8" burner with a proper albeit tiny three part flame? 1/4"???


Points to ponder



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1/2" NA burners are pretty common, one of the three I have the jet size up front in memory. I don't know much about molecular physics, how the things interact other than the very basics. How small a burner can be would be a matter of experimentation for me.


Heck, I don't even know how small a mig contact tip I can get so I can't even guess. Of course using a mig tip for the jet is as much a matter of convenience and any superior performance attributes. Well, that's why I started using them, Mike Porter on the other hand says the long smooth mig tip makes a more laminar flow of propane and so better induction. sounds good to me but I can't say of my own education or research. What I do know is they work better than a hole drilled in a piece of pipe.


Commercially NA burners can be pretty small, under 3/8" but they're more refined with tapered tubes from the jet to the outlet.


Whoever wants to start experimenting, please post the specs, results, pics, etc. I'll be watching avidly.


Frosty The Lucky.

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The smallest I have is a nominal 1/2" unit, but it is a commercial gas mixer and the Venturi throat is 0.350". I don't see any reason why they could not be made considerably smaller.


These are 1/2", 3/4", 1", 1 1/2" and 2" and seem to scale very well.




The nominal size is the pipe thread which fits the gas mixer body. The Venturi part at the bottom of the picture is threaded the same as the pipe and adjustment of the air gap is by turning the knurled section to screw the Venturi closer to the jet for richer and further away for leaner.




This gives extremely sensitive control of the air:fuel ratio. In a 5" diameter chamber, 16" long, this 1/2" burner will allow setting at any temperature between Heat-Treating and Welding (just under 1400 degF to just over 2500 degF) using a size 30 Amal jet. As close as I can measure using drills as go/nogo gauges, the jet is between .020" and.021". I use a 0-60 PSI regulator.


If they made a 1/4" mixer in this series, I would certainly have a use for it.


Going small in the "real" world, I would expect the difficulty of manufacture to become a limitation long before the physics, though it would be much easier without the adjustable air gap.


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Those are cool looking burners. Who is the manufacturer, and what is the standard application of those burners?

They are Amal Atmospheric Injectors. As far as I can tell, they are intended for use with low-pressure gases (Inches of water column) and would originally have been supplied to OEMs. Amal were best known for making carburettors back when the world was young and Britain made motorcycles. They also made various other bits of industrial gas-train equipment.
I have used the 2" and 1 1/2" units for at least 20 years at work. The smaller ones were the obvious choice once I became interested in forging and heat-treating stuff.
Amal products are now available from Burlen Fuel Systems. I think they really wanted the carburettor side of the business and the other stuff just came along with it. They do not have the injectors in their online shop, but I've had no problem talking to them on the phone. When I have bought from them, it has been as a walk-in customer, so I cannot comment on their internet sales.
Brochure for the atmospheric injectors
Burlen homepage
Usual disclaimer; my only association with Amal or Burlen is as a customer.
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My bad. Yes I know plumbers torches and such technically have smaller tubes albeit the typical propane torch has a 1/2" or so diam nozzle with several small orifices to produce tiny individual flames.This is how it is dealing with the reduction in tube size to molecule size. I guess I should have clarified however I was really specifically wondering about home made burners that run using propane. How small of a propane burner can be made using similar parts as is used in a typical "hardware store" supplied burner. i.e "T" style, "Reil" style, "side-arm" etc. Not a model but actually holding a good neutral flame.


Side note: What is the smallest Ward Tee anyway? Regular for that matter...



Ok, I'll accept a lean burning flame ;) (Rich flame would be too easy. Its adding that bit of air where it gets tricky)



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